Electrostatic precipitator

ABSTRACT

An electrostatic precipitator comprising a plurality of collector partitions subdividing the space within a housing into a plurality of flow chambers and adapted to collect, by electrostatic force, particles forming a gas stream traversing the flow passages. To eliminate the detrimental effects of flameless combustion on reaction of the solid particles of oxygen, the partitions are formed by upright electrode strips having lateral edges which are hooked together loosely in the normal positions of these electrode strips which may forcibly engage one another to prevent distortion of the partition upon thermal deformation of the strips. The outermost strips are provided with rigid profile support members which are hooked around the edges of the outermost strips throughout the height thereof.

United States Patent [191 Gelhaar et al.

[ ELECTROSTATIC PRECIPITATOR [75] Inventors: Rolf Gelhaar, Bergen-Enkheim;

' Juergen Nitz, Neu-Isenburg; Kurt Ran, Frankfurt am Main, all of Germany [73] Assignee: Metallgesellschaft Aktiengesellschaft,

Frankfurt am Main, Germany 22 Filed: July 11, 1973 211 App]. No.: 378,343

[30] Foreign Application Priority Data July 13, 1972 Germany 2234368 [52] US. Cl. 55/148, 55/156 [51] Int. Cl B01d 3/45 [58] Field of Search 55/156, 154, 109, 112, 55/113, 114, 121, 130, 148

[ 5 6 References Cited UNITED STATES PATENTS 1.773.876 8/1930 Seipp 55/130 X 1,903,640 4/1933 Wintermute 55/130 X 3,008,541 ll/l96l Wachter 55/156 X 3,328,940 7/1967 Stevernagel 55/131 3,362,135 1/1968 Stevernagel 55/152 X 3,417,519 12/1968 Hitter 52/494 X 3,748,831 7/1973 Lagerdahl 55/141 X 3,755,991 9/1973 Steurnagel 55/112 [451 Apr. 16, 1974 FOREIGN PATENTS OR APPLICATIONS 963,109 7/1964 Great Britain 55/130 533,848 9/1931 Germany 55/121 OTHER PUBLICATIONS German Printed Application No. 1,158,043, printed ll-2863, 1 sheet drawing, 2 pages spec.) 11-28-63,

Primary Examiner-Dennis E. Talbert, Jr. Attorney, Agent, or FirmKarl F. Ross; Herbert Dubno [57] ABSTRACT An electrostatic precipitator comprising a plurality of collector partitions subdividing the space within a housing into a plurality of flow chambers and adapted to collect, by electrostatic force, particles forming a gas stream traversing the flow passages. To eliminate the detrimental effects of flameless combustion on reaction of the solid particles of oxygen, the partitions are formed by upright electrode strips having lateral edges which are hooked together loosely in the normal positions of these electrode strips which may forcibly engage one another to prevent distortion of the partition upon thermal deformation of the strips. The outermost strips are provided with rigid profile support members which are hooked around theedges of the outermost strips throughout the height thereof.

8 Claims, 6 Drawing Figures PATENTEDAYPR 16 I974 SHEET 2 OF 2 11' 1 Fig. 4A

ELECTROSTATIC PRECIPITATOR FIELD OF THE INVENTION Our present invention relates to electrostatic precipitators and, more particularly, to a collector electrode arrangement for an electrostatic precipitator.

BACKGROUND OF THE INVENTION In an electrostatic precipitator for the recovery of solid particles from a gas stream, it is convenient to provide the collectorelectrodes as a plurality of generally parallel and preferably upright conductive partitions'which define conductive partitions which define between them generally flat channels or flow paths for the gas stream. Corona-discharge electrodes in the form of wires or the like may be provided in arrays between the collector electrodes and a dust or particle collecting bin is formed below the collector electrodes. The collector electrode shed the accumulated dust and solid particles when vibrated by a rapper which pro vides impact at a rigid member of a structure attached to the electrodes.

In all such electrostatic precipitators, it is important to maintain the planarity of the collector electrodes since any distortion may cause a portion of a collector electrode to approach a corona-discharge electrode more closely than is desired and may result in a breakdown across the space between collector and discharge electrode. Of course to simply avoid the danger that the gap will close to an extent that such breakdown will occur by originally spacing the electrodes apart to a considerable extent, creates the disadvantage that the apparatus becomes less efficient and requires more space for a given volume of gas processed, solids recovered, etc.

Especially when the gases which are to be freed from their solids or dust contain particles from metallurgical plants, e.g. iron-or sintering plants, difficulties have arisen with respect to distortion of the partitions or electrode walls forming the collector means of the precipitator. This is because the particles accumulated on the collector surfaces are pyrophoric or other highly active matter and undergo localized flameless combustion to locally heat the collector electrodes.

When the collector electrodes are composed of coldrolled steel strips under considerable internal stress, the flameless combustion generates stress-relief temperatures and gives rise to local distortion in the form of twisting, bending or bulging, especially where the strips are relatively long and narrow. At certain points, the corona-discharge path between the collecting electrode strips and the discharge or ionizing electrodes is reduced and flash-over breakdown occurs at such locations of close approach of the collector electrodes to the discharge electrodes. It may thus be necessary to reduce the voltage level which may be employed and thus the degree of separation or efficiency is also reduced.

It has been found that distortion of the type produced by the thermo effect of flameless combustion in an electrostatic precipitator can be reduced if the ratio of the width of the strip to the height thereof is held to a minimum of 1:15 and preferably 1:10, and the strips are connected by strips or the like which on the one hand reduce the transverse deflectibility of the strip and, on the other hand, limit the free height of the strip over which distrotion can take place. However, the connecting strips introduce an element between the collecting plate and the corona-discharge electrode so that the gap between them is effectively reduced and a lower voltage must be selected if continuous arcing is to be avoided.

The interruption of the profile of the collecting electrode strip, moreover prevents vibration thereof so that shedding of the accumulated dust and particles is restricted and efiiciency is reduced. In practice, dust does collect at regions which are remote from those at which rapping is applied and the connecting elements may also create disturbance or vortices in the flowing stream which draw the dust particles from the surface of the collector plates or strips and cause entrainment of the dust particles. It will be readily apparent that systems in which the profile of the electrode strip is interrupted or the electrode strip is shortened excessively reduce the shedding efficiency or otherwise introduce difficulties in the overall operational characteristics of the electrostatic precipitator.

There are described in the literature systems in which each of the collector electrodes is formed by a plurality of laterally adjoining strips interconnected in a tongue and groove arrangement so that they lie in mutual contat over the entire length of the interfitting portions. As a consequence, there is a mutually damping of the vibrations of the strips as produced by the rapping and again a decrease in the effectiveness of the unit.

In all of these structures there is a danger of distortion or twisting at the free edges of the outermost electrode strips. The tongue and groove of conventional systems engage deeply and reduce the remaining width of the collecting space.

OBJECTS OF THE INVENTION The principal object of the present invention is to provide an improved collector electrode assembly for an electrostatic precipitator in which the aforedescribed disadvantages are obviated.

It is another object of the invention to provide an electrostatic precipitator whose collector electrode can be formed with cold-rolled strips in which distortion is a less significant problem than-heretofore.

It is a further object of the invention to provide a collector electrode arrangement for an electrostatic precipitator in which the effect of flameless combustion is reduced or eliminated.

SUMMARY OF THE INVENTION These objects and others which will become apparent hereinafter are obtained in accordance with the present invention, in a collector-electrode arrangement which comprises an upper support member, a lower support member and a plurality of geometrically identical profile cold-rolled metal strips affixed to the upper and lower members and having profile edges loosely interfitting fitting with one another. The invention resides in providing profile backing members along the outer edges of the two outermost strips to envelope the edge profiles thereof in a non-rotatable manner, the backing members being hooked around the edges of the outermost strips throughout the height thereof. The adjacent collector electrode strips of each wall or partition are loosely hooked into one another so that during normal operation and without thermal distortion there is no contact between the two adjacent electrode strips at their interfitting edge profiles.

The term hooking around is intended to define the relationship whereby the backing member is rotated and simultaneously shifted laterally over the outer edge of the outer strip upon insertion of the latter into the former or upon the mounting of the backing strip onto the profiled edge. In this sense, the width of the mouth of the backing strip in a plane perpendicular to the main electrode plane may be smaller than the width of the profiled outer edge at its maximum whereby the profiled edge of the strip cannot be withdrawn through the mouth in a direction parallel to this plane. Thus only the relative rotation and simultaneous lateral displacement will bring about effective interfitting of the hook-profile backing strip and the edge profile of the outermost strip.

According to an important feature of the invention, the mutually interfitting but initially non-contacting electrode strips are geometrically identical with one another but have been rotated relative to one another through 180 about an axis in the plane of the strip parallel to its longitudinal edge. This means that, although the profile strips are geometrically identical to one another, they lie alternately in opposite orientations and thus have opposite bending tendencies in response to thermal or mechanical strip. Since the edge profile of all of the strips may be generally J-shaped with inwardly opening mouths (i.e. the bight of the J opens toward the center of the electrode on which it is formed), and both bights open toward one another on the ame side of the electrode, rotation of two adjacent strips through 180 relative to one another, enables the J-shaped profiles at the edges of two adjoining strips to interfit with the short shank of each J recess, in the bight of the other.

This arrangement, in which the adjacent electrode strips are initially loosely hooked into one another becomes effective when a strip is distorted or twisted and tends to move out of the plane of the collecting electrode wall. The adjoining collecting electrode strips tend to seize each other to prevent such distortion.

The profiles backing members are held against rotation by a cross-beam extending perpendicularly to the plane of the collecting electrode and connecting a number of the backing strips together. The backing strips thus space the free edges of the collecting electrodes from one another. With this system, of course, distortions are minimized and structural elements in the flow path between the edges of the collecting electrode strips are omitted so that the aforedescribed disadvantages can be obviated. The structure enables cold-rolled electrode strips to be employed and is effective with electrode strips having a length up to the preferred maximum of meters. The profiled backing members only engage the profiled outer edges of the strips loosely in the absence of distortion and hence there is little impediment to vibration under normal operating systems.

DESCRIPTION OF THE DRAWING The above and other objects, features and advantages of the present invention will become more readily apparent from the following description, reference being made to the accompanying drawing in which:

FIG. 1 is a longitudinal cross-sectional view, partly in diagrammatic form, of the collector electrode of an electrostatic precipitator embodying the present invention;

FIG. 2 is a cross-sectional view taken along the line IIII of FIG. 1, the corona-discharge electrode array having been omitted.

FIG. 3 is a detail view corresponding to FIG. 2 and taken generally along the line [IIIII of FIG. 1, illustrating the interfitting of the packing strips and generally showing the edge profile of another embodiment of an electrode strip according to the invention;

FIG. 4 is a detail cross-section taken along the line IV-IV of FIG. 1 but illustrating diagrammatically the edge profile of a pair of electrode strips according to the invention wherein the profiles have the configuration shown in FIG. 3; and

FIG. 4A is a corresponding view using the strip of FIG. 3A.

SPECIFIC DESCRIPTION In FIG. 1 we show a collecting electrode for an electrostatic precipitator in which a plurality of individual collecting electrode strips 1, l are provided in mutually adjacent and interlocked relationship. The outermostelectrode strips are designated at 1' while the strips intermediate the outermost strips have been indicated at l.

The collecting electrode strips 1, l are cold rolled profiled steel strip have a height of 15 meters and are identical to one another with a symmetrical profile formed with recesses constituting a collecting space for the dust. The strips have reverse bent edges and the edges of the adjacent collecting strips are hooked one into the other (FIGS. 2 and 4).

The collector electrode strips are secured at their upper ends by strips 2 to a carrier 3 which rests on the housing structure of the electrostatic precipitator 4. At their lower ends, the collecting electrodes are connected to a common bar 5 which, in turn, is struck by a conventional rapping linkage. The vibration thereby transmits to the wall formed by the strips 1, 1' releases the accumulated dust which falls into a bin below the bar 5.

The free edges of the outermost strips 1 are embraced by profiled backing members 6 which loosely surround and have been hooked around the profiled outer edges.

As is apparent from FIGS. 2, 3 and 3A the profiled backing members cannot simply be pushed over the profiled edge portions of the collecting electrode strips 1' and must be hooked therearound by lateral insertion and rotation.

To prevent the backing members from turning back, they are secured at their top and bottom ends or at an intermediate locations to a cross-beam 7 which also serves to maintain the distance between adjacent walls.

In FIG. 2 we show one embodiment of a profiled cold-rolled electrode strip embodying the invention. The strips 1 or 1' may be subdivided into three longitudinally extending sections 1a, lb and 1c of trapezoidal cross-section and equal width. The altitude of each trapezoid may be equal to the height of the edge profiles Id and 1e along the longitudinal edges of each plate. The edge profile may be generally J-section members (see FIGS. 3 and 3A) and may be identical for the end members 1' and the inner members 1. As can be seen in FIG. 2, the second member from the left is identical to the left-hand end member l but is rotated relatively thereto through 180 about an axis lying in the plane of the electrode strip and extending parallel to the longitudinal edge. The alternate electrode strips 1' or 1 thus have the same orientation. The edges of adjoining strips are hooked together as shown in FIGS. 4 and 4A.

In FIG. 4, for example, the edge profiles are .l-section members in which the bight 1/1 is generally planar and includes an obtuse angle a with the adjoining web portion 1r, the shank 1k including an acute angle B with the base 1h. The angle [-3 is some degrees less than that of the supplementary angle to angle a so that the shank 1k converges toward the web Hi to define a mouth 1m whose width is less than the altitude In of the profile.

A similar construction is provided for the edge profile of FIG. 4A in which, however, the bight 1h lies perpendicular to the web portion 1i. Again the two edge profiles are hooked into one another.

For the outer edge profiles seen in FIGS. 3 and 3A, there are provided the aforementioned backing members of a corresponding profile as will be described in greater detail hereinafter. The plates 1 shown in FIGS. 3 and 3A, however, are formed with narrow trapezoidal ribs 1a with a transverse spacing equal to a multiple of the transverse width of each rib. Of course, other corrugated patterns may be used to form the dust-catching pockets and web-stiffening members of the collecting electrode sheets.

The edge profile of the electrode strip 1 shown in FIG. 3 has an altitude 11 which is greater than the effective width 12 of the mouth of backing member 6. The latter is generally of U-configuration having a bight 13 connected to a bolt 14 which is received in a nut 15 to which the crossbar 7 is anchored. A double-nut arrangement in which a nut 15a is threaded onto the bolt 14 on one side of the bar 7 and is locked by a nut 15b threaded onto the other side, may also be used. A pair of shanks 16, 17 extend from the bight and are adapted to surround the profile 10, the shank 17 being bent as shown in FIG. 3 to allow the profile to be inserted in the direction of arrow 18 and then rotated around in the clockwise sense to fit the profile of the electrode strip into the profile backing member 6.

The profile backing member 6' of FIG. 3A likewise is similar to the edge profile 10 of the electrode strip with a mouth 12' having a width less than the altitude ll of the edge profile of the electrode strip so that again the edge profile must be inserted into member 6' and relative rotation is effected.

With all of the embodiments illustrated, a distortion or twisting of the collecting electrode strips causes the profiles of adjacent strips to seize one another whereby the individual collecting electrode strips on which flameless combustion has occurred cannot turn or move out of the plane of the plate wall. A lateral yielding of the outermost strips 1' is prevented by the profiled backing members 6 and 6, even in the case of strips having a height of 15 meters and the entire array of electrode strips remains generally planar.

We claim:

1. In an electrostatic precipitator, a collecting electrode comprising a generally planar array of substantially contiguous longitudinally extending collectingelectrode strips having edge profiles loosely hooked into the edge profiles of adjoining strips; means supporting said strips at the top thereof; a common rapping linkage connected to said strips at the bottom thereof, said strips including a pair of outer strips having outer edge profiles; respective profile backing members receiving said outer edge profiles and hooked therearound throughout the height of the electrode strips; and means for preventing relative rotation of said backing members and said outer edge profiles.

2. The. collecting electrode defined in claim 1 wherein said electrode strips are of geometrically similar configuration and alternate electrode strips are oriented with a rotation of to each other.

3. The collecting electrode defined in claim 2 wherein the last-mentioned means includes crossbeams secured to the backing members of a multiplicity of collecting electrodes in mutually spaced relation in said electrostatic precipitator.

4. The collecting electrode defined in claim 3 wherein said strips are profiled cold-rolled sheet metals and the edge profiles of each strip are of substantially .l-shaped cross-section with mouths opening toward one another on the same side of the strip.

5. The collecting electrode defined in claim 4 wherein said electrode strips are each formed with a plurality of longitudinally extending generally trapezoidal-section ribs between its edge profiles.

6. The collecting electrode defined in claim 4 wherein said edge profiles each include a bight extending away from a web portion of the respective strip and a shank including an acute angle with the respective bight and inclined toward the respective web portion, said backing members being of a profile generally similar to said edge profiles and being formed with mouths having a width less than the altitudes of the edge profile.

7. The collecting electrode defined in claim 6 wherein the bight includes an obtuse angle with the respective web portion.

8. The collecting electrode defined in claim 6 wherein said bight forms a right angle with the respective web portion. 

1. In an electrostatic precipitator, a collecting electrode comprising a generally planar array of substantially contiguous longitudinally extending collecting-electrode strips having edge profiles loosely hooked into the edge profiles of adjoining strips; means supporting said strips at the top thereof; a common rapping linkage connected to said strips at the bottom thereof, said strips including a pair of outer strips having outer edge profiles; respective profile backing members receiving said outer edge profiles and hooked therearound throughout the height of the electrode strips; and means for preventing relative rotation of said backing members and said outer edge profiles.
 2. The collecting electrode defined in claim 1 wherein said electrode strips are of geometrically similar configuration and alternate electrode strips are oriented with a rotation of 180* to each other.
 3. The collecting electrode defined in claim 2 wherein the last-mentioned means includes cross-beams secured to the backing members of a multiplicity of collecting electrodes in mutually spaced relation in said electrostatic precipitator.
 4. The collecting electrode defined in claim 3 wherein said strips are profiled cold-rolled sheet metals and the edge profiles of each strip are of substantially J-shaped cross-section with mouths opening toward one another on the same side of the strip.
 5. The collecting electrode defined in claim 4 wherein said electrode strips are each formed with a plurality of longitudinally extendinG generally trapezoidal-section ribs between its edge profiles.
 6. The collecting electrode defined in claim 4 wherein said edge profiles each include a bight extending away from a web portion of the respective strip and a shank including an acute angle with the respective bight and inclined toward the respective web portion, said backing members being of a profile generally similar to said edge profiles and being formed with mouths having a width less than the altitudes of the edge profile.
 7. The collecting electrode defined in claim 6 wherein the bight includes an obtuse angle with the respective web portion.
 8. The collecting electrode defined in claim 6 wherein said bight forms a right angle with the respective web portion. 